Are Cosmic Rays a Cause of Climate Change ?
Recent observations suggest that cosmic rays may play a significant role in the climate. In particular, satellite data have revealed a surprising correlation between cosmic ray intensity and the fraction of the Earth covered by low clouds. Since the cosmic ray intensity is modulated by the solar wind, this could provide an important clue to the long-sought mechanism connecting solar and climate variability. Moreover, if this connection were to be established, it could have significant consequences for our understanding of the solar contributions to the present global warming, since the cosmic ray intensity has fallen during the 20th century because of a more-than-doubling of the strength of the solar wind. In order to test whether cosmic rays and clouds are causally linked and, if so, to understand the microphysical mechanisms, a novel experiment known as CLOUD has been proposed at CERN. The talk will discuss the scientific case for a connection between cosmic rays and clouds, and describe the proposed CLOUD facility.